In the drilling and production of oil and gas wells, it is often necessary to obtain inner surface information concerning conditions present within the borehole. For example, tools and other objects may become lodged in the borehole during the drilling of a well. Such objects must be retrieved before drilling can continue.
In the operation and/or periodic maintenance of producing or injection wells, it is frequently necessary to obtain information about the construction and/or operating condition of production equipment located downhole. For example, detection of the onset of corrosion damage to well tubing or casing within a borehole enables the application of anti-corrosive treatments to the well. Early treatment of corrosive well conditions prevents the highly expensive and dangerous replacement of corrosion damaged well production components.
For performing other maintenance operations in a production well environment, such as replacement of various flow control valves or the inspection of the location and condition of casing perforations, it is highly desirable for an operator located at the surface to obtain accurate, real-time information about downhole conditions.
In fact, new regulations require operators of oilfields to perform a visual inspection of their safety/barrier valves after certain operations to verify cleanness to secure a further safe operation. These are often referred to as BlowOut Preventers (BOP) which are large, specialized valves or similar mechanical devices, usually installed redundantly in stacks, used to seal, control and monitor oil and gas wells, and intended to prevent tubing (e.g. drill pipe and well casing), tools and drilling fluid from being blown out of the wellbore (also known as borehole, the hole leading to the reservoir) when a blowout threatens.
Other tubulars may need inspection. This is the case of risers, large tubulars connecting Oil and Gas exploration or production platforms or ships to subsea installations.
Logging in environments as described above involves inserting an apparatus with sensors into the pipe and lowering it towards the oil and/or gas reservoir. The lowering means may be an installation on a platform like a winch with a wire or a free standing lowering means. The lowering means involve means for indication of the depth of the apparatus. The sensors built into the apparatus may measure temperature, pressure and/or other variables of interest. In combination with the depth these values are plotted graphically and may be compared to other graphs of an ideal or wanted case in order to evaluate the condition of the pipe. A temperature or pressure variance may indicate that something is wrong with the pipe, and the correct measures can be taken.
To improve the logging process visual inspection tools have been introduced. For example, EP0846840 describes a capsule that employs a method with both optical equipment for an end view and for a side view, which may record and send pictures of the inner surface of the pipe to an operator. The first optical equipment is positioned directly downwards while the second optical equipment is placed perpendicular to the first, facing directly to the inner wall. The tool is inserted in the pipe and is lowered as described above.
Because of the camera positions, the visual logging inspection tool described above may however not visualize the entire inside of the pipe in a continuous manner. To get a full 360/180 degree view, visual representation of the pipe wall and to ensure that no relevant area is potentially overseen, the tool have to be stopped and rotated regularly. This makes it both difficult and time consuming to inspect the inner wall of a well pipe if it is not known exactly what abnormalities to look for, and where in the well pipe to look for them. Thus, important areas of the well pipe may be overseen.